This invention relates to lighting systems and more particularly to an improved lighting system in which power distribution to lighting fixtures is easily modified to meet changing requirements.
Fluorescent lighting fixtures are generally used for illuminating floor areas in commercial buildings due to their efficiency as compared to other light sources, although other types of light sources such as incandescent lamps or high intensity discharge (HID) lamps or a combination of different types of light sources may be used. In modern construction of commercial buildings such as store and office buildings, ceiling structures generally comprise suspended ceilings. The space above the suspended ceiling is used for distribution of conditioned air and electrical power to the area below the ceiling. Where the area consists of a large open area such as in a large retail store, lighting fixtures may be suspended from a grid structure which supports the suspended ceiling. However, lighting fixtures of this type are not economical or pleasing in appearance where the floor space is to be divided into a number of offices and where the ceiling is relatively low. In such cases, lighting fixtures are typically recessed into the suspended ceiling such that a light diffusing grid on each fixture is positioned substantially coplanar with the ceiling. In many cases, the suspended ceiling is installed prior to partitioning a floor area into individual office spaces. The use of recessed fluorescent lighting fixtures for lighting the floor area facilitates partitioning the floor area into office spaces either without moving or with a minimum of moving the lighting fixtures which are recessed into the ceiling. After the floor area is partitioned into the individual offices, the lighting fixtures often must be rewired to permit switching the fixtures in each office independent of the fixtures in the remaining offices. Rewiring of the fixtures adds considerably to the expense of installing the lighting system. This expense is normally borne by the lighting contractor who must bid competitively for a contract to install and modify the lighting system. However, the contractor must place his bid without knowing his actual modification expenses since at the time the bid is placed, the contractor may have no information on the final floor plan for the building for which he is placing the bid.
U.S. Pat. No. 3,719,768 which issued on Mar. 6, 1973 to Nils G. Jonsson discloses one system which facilitates wiring of a lighting system when room partitions are installed. In the system disclosed in the Jonsson patent, flexible electrical cords are used for connecting electrical switches and outlets mounted in wall panels with power distribution boxes and control relays located above a suspended ceiling. The power distribution boxes and relays are also connected to lighting fixtures. The Jonsson system has the advantage of providing prewired wall panels which may be readily installed for partitioning a floor area into office spaces. However, the physical wiring above the suspended ceiling must be modified when the wall panels are installed to interconnect all lighting fixtures over a partitioned office with the wall switch. Considerable labor is still required for modifying the wiring when the wall partitions are installed. Another prior art system is shown in U.S. Pat. No. 3,683,101 which issued on Aug. 8, 1972 to Milton Liberman. In the Liberman system, prewired lighting fixtures are plugged into prewired receptacles on channels which are integral with some of the inverted tee support members for a suspended ceiling. Installation of a system of this type requires less labor over systems which are entirely wired on the site. However, connections to the wiring in the channels must be changed when switching requirements change, as when a space below the suspended ceiling is partitioned. Furthermore, the prewired channels do not readily adapt to the switching power to some fixtures plugged into a channel while leaving unswitched other similar fixtures plugged into the same channel, unless separate wires are run to each channel receptacle.